1. Field of the Invention
The present invention relates to a liquid crystal display (LCD) device and more particularly to a light emitting diode (LED) assembly having a small size and an LCD device having a thin profile.
2. Discussion of the Related Art
The LCD device, which uses an optical anisotropy and a polarization property to display an image, is widely used for notebook computers, monitors, TV, and so on, because of their high contrast ratio and characteristics adequate to display moving images.
The LCD device includes a liquid crystal panel having a first substrate, a second substrate and a liquid crystal layer. The first and second substrates face each other, and the liquid crystal layer is interposed therebetween. An arrangement of the liquid crystal molecules in the liquid crystal layer is changed by an electric field induced in the liquid crystal panel to control light transmissivity.
Generally, an additional light source is required because the LCD panel is a non-emissive-type display device. Accordingly, a backlight unit is disposed under the LCD panel. The LCD device displays images using light produced by the backlight unit and supplied to the LCD panel.
FIG. 1 is a cross-sectional view of the related art LCD device. In FIG. 1, the LCD device includes a liquid crystal panel 10, a backlight unit 20, a main frame 30, a top frame 40 and a bottom frame 50.
The liquid crystal panel 10 includes a first substrate 12, a second substrate 14 and a liquid crystal layer (not shown). The first and second substrates 12 and 14 face each other, and the liquid crystal layer is interposed therebetween. First and second polarization plates 19a and 19b is disposed on opposite sides of the liquid crystal panel 10.
The backlight unit 20 is disposed under the liquid crystal panel 10. The backlight unit 20 includes a light source 29, a reflective sheet 25, a light guide plate 23 and an optical sheet 21. The light source 29 is arranged along at least one side of the main frame 30. The reflective sheet 25 is disposed on the bottom frame 50 and has a color of white or silver. The light guide plate 25 is disposed on the reflective sheet 25, and the optical sheet 21 is disposed on or over the light guide plate 23.
The liquid crystal display panel 10 and the backlight unit 20 are combined using the main frame 30 that can prevent movement of the liquid crystal panel 10 and the backlight unit 20. The top frame 40 cover edges of the liquid crystal panel 10 and sides of the main frame 30, so the top frame 40 can support and protect of the edges of the liquid crystal panel 10 and sides of the main frame 30. The bottom frame 50 covers back edges of the main frame 30, so the bottom frame 50 is combined with the main frame 30 and the top frame 40 for modulation.
One of a cold cathode fluorescent lamp (CCFL), an external electrode fluorescent lamp and an LED is used as a light source 29 of the backlight unit 20. Among these light sources, the LED is widely used because of their characteristics, for example, small size, low power consumption, and so on.
As shown in FIG. 1, the LED 29a is arranged on a printed circuit board (PCB) 29b to form the light source 29. The light source 29 including the LED 29a may be referred to as an LED assembly. The light emitted from at least one LED assembly 29 is provided into the light guide plate 23. The light is processed into a plane light source having an uniform brightness through the light guide plate 23, the reflective sheet 25 and the optical sheet 21, and provided into the liquid crystal panel 10.
FIG. 2 schematically shows the related art LED assembly. As shown in FIG. 2, a plurality of LEDs 29a are arranged on a PCB 29b, and input lines 27a and output lines 27b are formed on the PCB 29b. In addition, a plurality of pads 28 are formed at one end of the PCB 29b. The input lines 27a and the output lines 27b are electrically connected to an LED driving circuit (not shown) to drive the LEDs 29a. 
There are some problems in the related art LCD device and the LED assembly. More LEDs 29a are required as a size of the LCD device is increased. For example, LEDs more than several hundreds are used for an LCD device of 42 inches. In this case, it is very difficult to supply a driving voltage with all LEDs connected in series. Accordingly, some LEDs form one array, and the LEDs in one array are electrically connected in series. As a result, the plurality of pads 28 should be formed on the PCB 29b as shown in FIG. 2.
To avoid an electrical short and an electrical interference, the input lines 27a are disposed one side of the PCB 29b and the output lines 27b are disposed another side of the PCB 29b. Namely, as shown in FIG. 2, the input lines 27a are disposed at an upper side of the LEDs 29a, and the output lines 27b are disposed at a lower side of the LEDs 29a. As a result, the LEDs 29a are positioned at a center line of the PCB 29b. 
On the other hand, since the LEDs 29a should correspond to a center of the light guide plate 23 as shown in FIG. 1, a lower side of the PCB 29b protrudes than the light guide plate 23 or the reflective sheet 25. As a result, a protruding portion “A” is required in the bottom frame 50 to cover the lower side of the PCB 29b such that a thickness “d1” of the LCD device is increased. Particularly, since the input lines 27a and the output lines 27b should be disposed at opposite sides of the PCB 29b, the PCB 29b has a width “d′1” of about 6.0˜8.0 mm.
When the width “d′1” of the PCB 29b is increased, the thickness “d1” of the LCD device is also increased. In addition, a weight of the LCD device is increased.
Recently, a method of connecting the input lines and the output lines through via holes is introduced. Unfortunately, since the PCB requires a plurality of layers, weight of the PCB is rapidly increased. Accordingly, new LED assembly having advantages on the width as well as the weight is required.